The objectives are to provide the applicant with a solid molecular biology base on which to build a productive independent research career and to begin to understand some of the mechanisms of control of gene expression. The bovine prolactin 5' flanking region will be used in transfection studies and in transgenic mice to study the regulation of cell-specific expression and the hormonal and developmental modulation of the prolactin gene. The bovine prolactin gene has been cloned and characterized in the primary sponsor's laboratory. The 5' flanking region containing the prolactin promoter has been linked to a chloramphenicol acetyltransferase (CAT) gene to allow convenient study of the promoter in transient expression assays. These experiments provide preliminary evidence of tissue-specific expression of CAT directed by the 1000 bp prolactin 5' flanking region. This region contains the DNA sequences required for regulation by epidermal growth factor and dexamethasone. The ability to introduce cloned sequences into the germ line of mice provides a means of studying sequences necessary for tissue-specific expression and hormonal/developmental regulation in an in vivo setting. The transgenic mouse model of controlled gene expression will then allow investigation of the effects of oncogene expression in a tissue-directed fashion and permit determination of the roles of developmental and hormonal control on tumor development in transgenic mouse system.